Dentistry has used light curable composite resins for over 20 years with great success for preparing restorations, cementation of restorations, and a number of other dental restorative procedures such that light curing is now a standard procedure in dentistry.
Initial curing lights consisted of halogen devices, first with light sources removed from the point of application and thereafter with light transmitted to the point of application through long fibers. Following that, light curing guns were introduced. These devices typically used halogen light sources with short fused fiber optic light guides close to the lamp to apply high intensity light at the point of application. Along the way, radiometers were introduced into the dental profession for the purpose of measuring light output as a means of assessing the curing light's ability to properly polymerize the dental restorative materials.
Halogen curing lights suffer from a wide variety of mechanisms that cause degradation of intensity. These mechanisms include loss of light output from the halogen lamp, filter degradation, buildup of resin on light guides, degradation of light guides due to sterilization and faulty voltage control circuitry. The radiometer, therefore, has become widely accepted as a means of assessing light output of these devices and indirectly determining whether or not a material or restoration will be properly polymerized.
The popular radiometers in dentistry use either silicon or selenium detector cells with filters that block energy outside of the 400–500 nanometer range. Initially, radiometers were developed specifically for use with halogen light sources with their filters matched fairly closely to the wavelength distribution of the curing lights themselves. In recent years, other types of light sources have been introduced, namely plasma arc or gas pressure lamp devices, using xenon lamps to produce high intensity light in the 400–500 nanometer range. More recently, light emitting diodes (LED's) have been used to produce light specifically peaking at 470, 450 or 420 nanometers that match the absorption characteristics of photoinitiators currently used in dentistry to polymerize these restorative materials. However, when one uses a different light source on the same radiometer designed for halogen usage, erroneous readings result. Accordingly, to properly use a radiometer, the radiometer must be calibrated for use relative to a given light source and no standard of comparison exists to permit comparing the results between radiometers calibrated for different light sources.
The National Institute of Standards and Technology (NIST) presently requires every radiometer to be designed specifically for the light source it's being used with. Moreover, even if one were to use a separate radiometer designed specifically for each of the three types of light sources currently used in dentistry, the problem would still remain as to how long to expose the material under a given set of conditions i.e. depth, shade, and type of material.
Researchers in the dental field typically use a sensitive analytical laboratory tool employing a technique called Fourier Transform Infrared Spectroscopy (FTIR) to determine when a light curable material is maximally polymerized by measuring the ratio of aliphatic carbon-to-carbon double bonds pre- and post-exposure. Such laboratory equipment costs thousands of dollars and is clearly beyond the practical needs of the clinical dentist It would therefore be desirable to have a simple radiometer device that can assess the degree of polymerization and not be affected by which type of light source is used. It would further be desirable for the dentist to be able to determine the exposure time necessary to effect maximal polymerization of the restorative material selected for use in the preparation of a given restoration independent of the light source used to cure the material.